- Previously enrolled for the same procedure or the same pain generator site. (For example, this would exclude a patient who had an intra-articular facet joint injection at the right L5/S1 if: 1) he had the same injection 3 months ago and was enrolled at that time, or 2) the patient was already enrolled for a medial branch block at the right L5 and sacral ala, as this targets the same facet joint.)